Many vehicles utilize drivetrain configurations where ground speed is directly coupled to engine speed, such that in order to obtain very low ground speeds, low engine speeds are required. In situations where engine speed is initially low, an increase in load on the engine can result in an engine stall.
During various grading operations, a motor grader may experience a sudden increase in drawbar load. As a result of the increase in loading, engine speed will decrease and the rimpull will increase. If the operator cannot reduce the load quickly enough, tire slip may occur.
Operating at the same ground speed in a higher gear gives the operator more ground speed feedback and more engine speed feedback, aiding the operator to prevent tire slip. The higher gear also limits the rimpull of the machine, further helping to prevent tire slip. A consequence of running in a higher gear at a lower engine speed is that the engine is less responsive and more susceptible to stalling. Furthermore, emissions reduction controls may reduce the ability of the engine to respond quickly enough to such transient loads and prevent engine stall.
Therefore, it would be desirable to operate the engine at a higher engine speed but in a lower gear while maintaining the same ground speed behavior as the higher gear. In doing so, the machine can behave as if it is operating in a higher gear, shifting automatically to maintain optimal engine speed.